This invention generally relates to zoom lenses and, more particularly, to zoom lens systems in which zooming action and focusing are effected by relative movement across the optical axis of selectively deformed non-rotational plates that are themselves arranged in pairs spaced along the optical axis.
As is well known, a zoom lens is one in which the focal length can be varied continuously by moving one or more of the lens components along the axis, the image position being maintained in a fixed plane by some means, either optical or mechanical. They were originally developed to fulfill the need in the motion picture and television industries to be able to simulate tracking shots without having to actually move a camera. This, of course, required an optical system capable of continuously changing the scale of the scene from some fixed vantage point while at the same time conveniently keeping the image in focus as it changed in size at a fixed location behind the lens corresponding to either the film plane or the plane of some photosensitive device such as a vidicon tube.
Since image scale is proportional to equivalent focal length zoom systems necessarily are those of continuously adjustable equivalent focal length. And, since equivalent focal length is a function of the individual focal lengths of the components of a lens and the axial spacing between them, a continuous variation in equivalent focal length has been traditionally achieved by causing one or more of the component spacings to vary. Thus, the underlying basis for changing image scale in known zoom systems is to change at least one spacing between the series of positive and negative components which usually comprise the lens. This, however, also alters the lens-to-image distance for maximum sharpness. Consequently, altering component spacing, while achieving changes in image scale, also without additional compensation introduces changes in focus throughout the zooming action. Focus change can be compensated for by changing the lens-to-film plane distance and re-positioning the film plane may be preferred if the lens is large and the film plane easier to move. However, this is not usually done in the true zooming system, but where it is, the systems are referred to as varifocal.
In the true zoom lens, other forms of compensation are traditionally employed. These have been mentioned previously, and one is referred to as mechanical and the other as optical.
With mechanical compensation, the movement of the components responsible for the change in equivalent focal length is linked with the movement of another component or components whose movement in turn compensates in advance for the potential change of back focus and thus maintains the image acceptably sharp throughout some zoom range, the ratio of maximum to minimum equivalent focal length. Since the two movements are unequal, they are typically linked by a cam arrangement which forces their correct functional movement.
In optically compensated zoom lenses, two or more components are connected so that they travel together over the same distance to keep the image sharp at the various focal length settings of the zoom lens.
Beyond these basic arrangements, zoom lenses become more complex as the zooming requirements increase. This comes about because of the need to have additional components for aberration control, a problem which becomes increasingly difficult with increases in the zooming range. Thus, the general trend is for zoom lenses to contain more components and become more complex and expensive as zoom ratios become higher.
Another consideration in the design of zoom lenses is the desirability of maintaining constant image illumination throughout the range of operation. This requires compensation for changes in the relative aperture introduced by changes in the focal length. Here again, mechanical compensation, but in the form of a variable diaphragm, is often used to solve the problem so that there is no need for making exposure time adjustments because of changing aperture conditions. The favored approach, however, is to use an afocal zoom section ahead of an imaging system in which the aperture remains constant. Here, the afocal attachment is made to change image scale with its aperture matching or exceeding the aperture of the imaging portion so that changes of magnification in the afocal zoom section do not affect the relative aperture of the overall lens. Many recent systems incorporate the stop even into the zoom portion as long as it stays ahead of the fixed part of the zoom and is not interfered with by the zoom action. The stop that is put that far into the zoom system in terms of its image will still have the same aperture ratio at the final image, which is all that is required. That is, the exit pupil is fixed in size and location.
Other features which are known to have been used in zoom lenses include automation of the zooming action as well as remotely controlled zooming action. It is also known to adapt zoom lenses for use in still cameras, which usually have larger formats and field angles than movie cameras.
Thus, multicomponent zoom lenses are wellknown in the art and are more or less elaborate, depending primarily on the zoom ratio requirements. However, all are in principle based on the fundamental idea that image scale changes can be brought about by changing the spacing between the various components, positive, negative, or both, to achieve the necessary optical power changes along with compensation for shifts in back focal length.
It is the primary object of the present invention to provide the art with zoom lenses which are based on quite another type of lens motion to affect the optical power changes needed for zooming action and focusing. This new action involves the movement of distorted pairs of plates across, rather than along, the optical axis as in the prior art and represents a novel approach to zooming action and focusing which exploits the optical properties of transversely movable deformed plates.
In 1967 in U.S. Pat. No. 3,305,294, Luis Alvarez described a pair of distorted surfaces defined mathematically with a cubic equation and movable across the optical axis to produce a continuously variable dioptric power that simulated the action of rotationally symmetric shaped dioptric lenses.
In 1971, James G. Baker in U.S. Pat. No. 3,583,790 pointed out that the addition of higher-order terms, particularly the fifth, provides aberration control in addition to the focusing action introduced by Alvarez and presented refined embodiments shown in 1984 in his U.S. Pat. No. 4,457,592.
U.S. Pat. No. 4,650,292 of James G. Baker and William T. Plummer describes the geometry of a pair of distorted surfaces which can be rotated across the optical axis about an offset axis parallel to the optical axis to achieve focusing action and aberration control.
However, none of the literature to date suggests the use of such deformed plates for combined zooming and focusing purposes. As will be seen, the present invention exploits the properties of transversely movable plates to achieve zooming action and focusing in a variety of ways.
Other objects of the invention will in part be obvious and will in part appear hereinafter. Accordingly, the invention comprises the optical elements and systems possessing the construction, combination and arrangement of elements which are exemplified in the following detailed description.